It is widely recognized that the efficiency and energy output of a gas turbine engine can be improved by increasing the operating temperature of the turbine. Under elevated operating temperatures, gas turbine engine components such as the turbine rotors and blades are cooled by a flow of compressed air discharged at a relatively cool temperature. The flow of coolant across the turbine rotor and through the interior of the blades removes heat so as to prevent excessive reduction of the mechanical strength properties of the blades and rotor.
Therefore on the one hand the turbine operating temperature, efficiency and output of the engine are limited by the high temperature capabilities of the various turbine elements and the materials of which they are made. In general the lower the temperature of the elements the higher strength and resistance to operating stresses. On the other hand the performance of the gas turbine engine is very sensitive to the amount of air flow that is used for cooling the hot turbine components. The less air that is used for cooling functions the better the efficiency and performance of the engine.
To cool the turbine blades, a flow of cooling air is typically introduced. There are two ways to deliver cooling air to turbine blades. One is from stationary part and other is from rotating part. From a stationary part, the cooling flow is introduced with a swirl or tangential velocity component through use of a tangential on board injector with nozzles directed at the rotating hub of the turbine rotor. From a rotating part, a flow of cooling air is typically introduced at a lower radius as close as possible to the engine shaft, such as underneath of the rotor disk bore.